Conventionally, a decentralized power supply grid-connected with a commercial power system by using an inverter device has been developed for practical use. In such a power supply system, an inverter device converts direct-current power of a direct-current power supply such as a solar battery, a storage battery, or an electric generator into alternating-current power, and supplies the converted alternating-current power to each household electrical appliance (household load). If power output from the inverter device is less than power to be consumed by the household load, power is purchased from a power company by allowing power to flow from a commercial power system to cover a shortage of power. In contrast, if power output from the inverter device exceeds power to be consumed by the household load, it is also possible to sell power to the power company by allowing power to flow to the commercial power system. As such, an operation mode of the inverter device in which the inverter device is interconnected with the commercial power system and supplies power to the load is referred to as a “grid-connected operation mode”.
As to the inverter device as described above, when one wishes to use the inverter device as an emergency power supply or an independent power supply in the case where some failure occurs in the commercial power system owing to power outage or the like, some inverter devices can be disconnected from the commercial power system so that only the power output from the inverter devices can be supplied to some load (isolated load) connected to a dedicated receptacle. As such, an operation mode of the inverter device in which the inverter device is independent of the commercial power system and supplies power to the load is referred to as an “isolated operation mode”.
A conventional inverter device in the case where a solar battery is used as a direct-current power source will be described with reference to FIG. 5.
FIG. 5 is a functional block diagram showing a configuration of a decentralized power supply system using a conventional inverter device.
An inverter device 102 includes a converter 103, an inverter 104, a filter 105, a protection relay 106, an interconnection relay 107, a control unit 108, and an isolated relay 116. Control unit 108 is also controlled by a signal from outside, such as from a remote controller 109.
A voltage of direct-current power from a solar battery array 101 is boosted by converter 103. The direct-current power, whose voltage is boosted, is converted into alternating-current power in inverter 104. A harmonic component of the converted alternating-current power is smoothed in filter 105. In the grid-connected operation mode, the alternating-current power converted in inverter device 102 is supplied to a household load (not shown) in a manner interconnecting with a commercial power system 114. At that time, isolated relay 116 is brought into a non-conduction state, while each of protection relay 106 and interconnection relay 107 is brought into a conduction state.
In contrast, in the isolated operation mode, either of protection relay 106 and interconnection relay 107 are brought into a non-conduction state, and isolated relay 116 is brought into a conduction state, so that inverter device 102 is disconnected from commercial power system 114. Accordingly, the alternating-current power converted in inverter device 102 is supplied from a dedicated, isolated load connecting extension receptacle 110 to the isolated load.
As described above, in the conventional inverter device 102, a power supply line for alternating-current power output from inverter 104 is provided for each of the grid-connected operation and the isolated operation (see Patent Document 1 and Patent Document 2).
Patent Document 1: Japanese Patent Laying-Open No. 9-135577
Patent Document 2: Japanese Patent Laying-Open No. 2001-238464
In the conventional inverter device 102 as described above, interconnection relay 107 which allows alternating-current power output from inverter 104 to be in a conduction state/non-conduction state in the grid-connected operation mode, and isolated relay 116 which allows alternating-current power output from inverter 104 to be in a conduction state/non-conduction state in the isolated operation mode, are provided in parallel. It was therefore difficult to reduce the dimension of a body of inverter device 102.
Furthermore, in Patent Document 1, an output terminal for outputting alternating-current power converted by inverter 104 in the isolated operation mode is provided at a body surface of inverter device 102. Therefore, when one wishes to use a load at a place remote from inverter device 102, one inevitably has to connect dedicated, isolated load connecting extension receptacle 110 thereto.
An aspect of the present invention is made to solve such a problem above. An object of the present invention is to provide an inverter device performing a grid-connected operation with an output plug inserted into a household receptacle, the inverter device allowing the output plug and a load-connecting receptacle for the isolated operation to be used with a simple configuration.